DESCRIPTION (Investigator's Abstract): Accurate localization of electrical sources in the brain has many important clinical and research applications. An ideal tool for localizing sources in the brain are non- invasiM EEC's measured on the scalp. While methods to localize sources in the brain using scalp EEC's have been developed, these methods have not been used under optimal conditions. In part, this is because only limited information about optimal conditions for scalp EEC's is available. Therefore, a major goal of this research project is to determine optimal conditions for using scalp EEC's and the improvement in localization accuracy that can be achieved using these EEC's under such conditions. This project would also develop methods for using epidural and depth (intracerebral) EEC's for source localization. while theory indicates that these EEC's should provide more accurate localization than scalp EEC's, this advantage has not been investigated or experimentally demonstrated. The localization accuracy that can be achieved using scalp EEC's in combination with a limited number of epidural and/or depth EEC's would also be investigated to determine which combinations provide the greatest accuracy with the least number of invasive depth and/or epidural electrodes. These investigations will be performed using implanted sources in the brain. Since the locations of these sources can be exactly determined from CT's, N1RI's, and/or X- rays, the accuracy of the localization methods can be exactly determined. The methods of using scalp, epidural, and/or depth EEC's to obtain optimal localization accuracy of electrical sources in the brain would be applied to the localization of epileptic foci and other sources in the brain. At present, invasive depth EEC electrodes must be surgically implanted in the brains of some epilepsy patients being investigated for surgical treatment of their disorder. A major goal of this research is to provide localization methods which will eliminate or at least reduce the use of invasive depth electrodes in the investigation and treatment of this disorder. The lacalization methods to be developed in this research would also provide improved localization accuracy for other sources in the brain, such as evoked sources for both clinical and research purposes.